Toxicity and phototoxicity of mixtures of highly lipophilic PAH compounds in marine sediment:: Can the ΣPAH model be extrapolated?

The additivity of toxic units was tested using sediments contaminated with mixtures of highly Lipophilic (log K-OW > 4.5) parent and alkylated PAHs. The direct toxicity and photoinduced toxicity of these mixtures were examined in standard 10-day sediment toxicity tests using the infaunal amphipod Rhepoxinius abronius, with mortality and the survivors' ability to rebury as endpoints. Survivors of the initial 10-day tests were then exposed for 1 h to ultraviolet (UV) radiation and the results compared to initial (10-day) endpoints. Tissue residues and lipids were measured and biota-sediment accumulation factor (BSAF) values determined. The results indicated that the bioaccumulated contaminants were not initially toxic, however, they were highly phototoxic. Although the summed toxic units of these contaminants appeared to be nonadditive, additivity was not disproved as inaccuracies in extrapolating the K-OW-LC50 QSAR or insufficient exposure duration might also have accounted for the observed results. Critical body residue (CBR) estimates for R. abronius were similar while BSAF values were much larger(10X) in comparison to other studies, which used amphipods and PAHs. The phototoxicity of mixtures of contaminants were similar to the phototoxicity of single contaminants when expressed on a molar basis, which suggests that phototoxicities may be roughly additive.